Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 ============= 2 PHY subsystem 3 ============= 4 5 :Author: Kishon Vijay Abraham I <firstname.lastname@example.org> 6 7 This document explains the Generic PHY Framework along with the APIs provided, 8 and how-to-use. 9 10 Introduction 11 ============ 12 13 *PHY* is the abbreviation for physical layer. It is used to connect a device 14 to the physical medium e.g., the USB controller has a PHY to provide functions 15 such as serialization, de-serialization, encoding, decoding and is responsible 16 for obtaining the required data transmission rate. Note that some USB 17 controllers have PHY functionality embedded into it and others use an external 18 PHY. Other peripherals that use PHY include Wireless LAN, Ethernet, 19 SATA etc. 20 21 The intention of creating this framework is to bring the PHY drivers spread 22 all over the Linux kernel to drivers/phy to increase code re-use and for 23 better code maintainability. 24 25 This framework will be of use only to devices that use external PHY (PHY 26 functionality is not embedded within the controller). 27 28 Registering/Unregistering the PHY provider 29 ========================================== 30 31 PHY provider refers to an entity that implements one or more PHY instances. 32 For the simple case where the PHY provider implements only a single instance of 33 the PHY, the framework provides its own implementation of of_xlate in 34 of_phy_simple_xlate. If the PHY provider implements multiple instances, it 35 should provide its own implementation of of_xlate. of_xlate is used only for 36 dt boot case. 37 38 :: 39 40 #define of_phy_provider_register(dev, xlate) \ 41 __of_phy_provider_register((dev), NULL, THIS_MODULE, (xlate)) 42 43 #define devm_of_phy_provider_register(dev, xlate) \ 44 __devm_of_phy_provider_register((dev), NULL, THIS_MODULE, 45 (xlate)) 46 47 of_phy_provider_register and devm_of_phy_provider_register macros can be used to 48 register the phy_provider and it takes device and of_xlate as 49 arguments. For the dt boot case, all PHY providers should use one of the above 50 2 macros to register the PHY provider. 51 52 Often the device tree nodes associated with a PHY provider will contain a set 53 of children that each represent a single PHY. Some bindings may nest the child 54 nodes within extra levels for context and extensibility, in which case the low 55 level of_phy_provider_register_full() and devm_of_phy_provider_register_full() 56 macros can be used to override the node containing the children. 57 58 :: 59 60 #define of_phy_provider_register_full(dev, children, xlate) \ 61 __of_phy_provider_register(dev, children, THIS_MODULE, xlate) 62 63 #define devm_of_phy_provider_register_full(dev, children, xlate) \ 64 __devm_of_phy_provider_register_full(dev, children, 65 THIS_MODULE, xlate) 66 67 void devm_of_phy_provider_unregister(struct device *dev, 68 struct phy_provider *phy_provider); 69 void of_phy_provider_unregister(struct phy_provider *phy_provider); 70 71 devm_of_phy_provider_unregister and of_phy_provider_unregister can be used to 72 unregister the PHY. 73 74 Creating the PHY 75 ================ 76 77 The PHY driver should create the PHY in order for other peripheral controllers 78 to make use of it. The PHY framework provides 2 APIs to create the PHY. 79 80 :: 81 82 struct phy *phy_create(struct device *dev, struct device_node *node, 83 const struct phy_ops *ops); 84 struct phy *devm_phy_create(struct device *dev, 85 struct device_node *node, 86 const struct phy_ops *ops); 87 88 The PHY drivers can use one of the above 2 APIs to create the PHY by passing 89 the device pointer and phy ops. 90 phy_ops is a set of function pointers for performing PHY operations such as 91 init, exit, power_on and power_off. 92 93 Inorder to dereference the private data (in phy_ops), the phy provider driver 94 can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in 95 phy_ops to get back the private data. 96 97 4. Getting a reference to the PHY 98 99 Before the controller can make use of the PHY, it has to get a reference to 100 it. This framework provides the following APIs to get a reference to the PHY. 101 102 :: 103 104 struct phy *phy_get(struct device *dev, const char *string); 105 struct phy *phy_optional_get(struct device *dev, const char *string); 106 struct phy *devm_phy_get(struct device *dev, const char *string); 107 struct phy *devm_phy_optional_get(struct device *dev, 108 const char *string); 109 struct phy *devm_of_phy_get_by_index(struct device *dev, 110 struct device_node *np, 111 int index); 112 113 phy_get, phy_optional_get, devm_phy_get and devm_phy_optional_get can 114 be used to get the PHY. In the case of dt boot, the string arguments 115 should contain the phy name as given in the dt data and in the case of 116 non-dt boot, it should contain the label of the PHY. The two 117 devm_phy_get associates the device with the PHY using devres on 118 successful PHY get. On driver detach, release function is invoked on 119 the devres data and devres data is freed. phy_optional_get and 120 devm_phy_optional_get should be used when the phy is optional. These 121 two functions will never return -ENODEV, but instead returns NULL when 122 the phy cannot be found.Some generic drivers, such as ehci, may use multiple 123 phys and for such drivers referencing phy(s) by name(s) does not make sense. In 124 this case, devm_of_phy_get_by_index can be used to get a phy reference based on 125 the index. 126 127 It should be noted that NULL is a valid phy reference. All phy 128 consumer calls on the NULL phy become NOPs. That is the release calls, 129 the phy_init() and phy_exit() calls, and phy_power_on() and 130 phy_power_off() calls are all NOP when applied to a NULL phy. The NULL 131 phy is useful in devices for handling optional phy devices. 132 133 Releasing a reference to the PHY 134 ================================ 135 136 When the controller no longer needs the PHY, it has to release the reference 137 to the PHY it has obtained using the APIs mentioned in the above section. The 138 PHY framework provides 2 APIs to release a reference to the PHY. 139 140 :: 141 142 void phy_put(struct phy *phy); 143 void devm_phy_put(struct device *dev, struct phy *phy); 144 145 Both these APIs are used to release a reference to the PHY and devm_phy_put 146 destroys the devres associated with this PHY. 147 148 Destroying the PHY 149 ================== 150 151 When the driver that created the PHY is unloaded, it should destroy the PHY it 152 created using one of the following 2 APIs:: 153 154 void phy_destroy(struct phy *phy); 155 void devm_phy_destroy(struct device *dev, struct phy *phy); 156 157 Both these APIs destroy the PHY and devm_phy_destroy destroys the devres 158 associated with this PHY. 159 160 PM Runtime 161 ========== 162 163 This subsystem is pm runtime enabled. So while creating the PHY, 164 pm_runtime_enable of the phy device created by this subsystem is called and 165 while destroying the PHY, pm_runtime_disable is called. Note that the phy 166 device created by this subsystem will be a child of the device that calls 167 phy_create (PHY provider device). 168 169 So pm_runtime_get_sync of the phy_device created by this subsystem will invoke 170 pm_runtime_get_sync of PHY provider device because of parent-child relationship. 171 It should also be noted that phy_power_on and phy_power_off performs 172 phy_pm_runtime_get_sync and phy_pm_runtime_put respectively. 173 There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync, 174 phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and 175 phy_pm_runtime_forbid for performing PM operations. 176 177 PHY Mappings 178 ============ 179 180 In order to get reference to a PHY without help from DeviceTree, the framework 181 offers lookups which can be compared to clkdev that allow clk structures to be 182 bound to devices. A lookup can be made be made during runtime when a handle to 183 the struct phy already exists. 184 185 The framework offers the following API for registering and unregistering the 186 lookups:: 187 188 int phy_create_lookup(struct phy *phy, const char *con_id, 189 const char *dev_id); 190 void phy_remove_lookup(struct phy *phy, const char *con_id, 191 const char *dev_id); 192 193 DeviceTree Binding 194 ================== 195 196 The documentation for PHY dt binding can be found @ 197 Documentation/devicetree/bindings/phy/phy-bindings.txt